[kitd]

Pre-v21, Java's threads were 1:1 based on OS threads. HFT apps were normally single-threaded with exotic work-dispatching frameworks, native-memory buffers &| built-in network stacks so, while being undoubtedly fast, were not particularly representative.

V21 virtual threads are more like Go's goroutines. They map 1:m with OS threads, and the JVM is responsible for scheduling them, making them much less of a burden on the underlying OS, with fewer context switches, etc. And the best thing is, there has been minimal change in the Java standard library API, making them very accessible to existing devs and their codebases.

[mongol]

Once upon a time, Java had "green threads". They were kind of like virtual threads, but the way I understood it was that they all mapped to one OS thread. While these new virtual threads map m:n to OS threads.